It is important to avoid unintentionally contacting a patient's nerves when performing surgical procedures, especially when using surgical tools and procedures that involve cutting or boring through tissue. Moreover, it is especially important to sense the presence of spinal nerves when performing spinal surgery, since these nerves are responsible for the control of major body functions. However, avoiding inadvertent contact with these nerves is especially difficult due to the high nerve density in the region of the spine and cauda equina.
The advent of minimally invasive surgery offers great benefits to patients through reduced tissue disruption and trauma during surgical procedures. Unfortunately, a downside of such minimally invasive surgical procedures is that they tend to offer a somewhat reduced visibility of the patient's tissues during the surgery. Accordingly, the danger of inadvertently contacting and/or severing a patient's nerves can be increased.
Systems exist that provide remote optical viewing of a surgical site during minimally invasive surgical procedures. However, such systems cannot be used when initially penetrating into the tissue. Moreover, such optical viewing systems cannot reliably be used to detect the location of small diameter peripheral nerves.
Consequently, a need exists for a system that alerts an operator that a particular surgical tool, which is being minimally invasively inserted into a patient's body, is in close proximity to a nerve. As such, the operator may then redirect the path of the tool to avoid inadvertent contact with the nerve. It is especially important that such a system alerts an operator that a nerve is being approached as the surgical tool is advanced into the patient's body prior to contact with the nerve, such that a safety distance margin between the surgical tool and the nerve can be maintained.
A variety of antiquated, existing electrical systems are adapted to sense whether a surgical tool is positioned adjacent to a patient's nerve. Such systems have proven to be particularly advantageous in positioning a hypodermic needle adjacent to a nerve such that the needle can be used to deliver anesthetic to the region of the body adjacent the nerve. Such systems rely on electrifying the needle itself such that as a nerve is approached, the electrical potential of the needle will depolarize the nerve causing the muscle fibers coupled to the nerve to contract and relax, resulting in a visible muscular reaction, seen as a “twitch”.
A disadvantage of such systems is that they rely on a visual indication, being seen as a “twitch” in the patient's body. During precision minimally invasive surgery, uncontrollable patient movement caused by patient twitching, is not at all desirable, since such movement may itself be injurious. In addition, such systems rely on the operator to visually detect the twitch. Accordingly, such systems are quite limited, and are not particularly well adapted for use in minimally invasive surgery.